The present invention relates to a film mirror for solar power generation and a composite film for use therein.
Sunlight reflectors are exposed to ultraviolet light and heat from sunlight, weather, sandy dust and the like, and therefore glass mirrors have conventionally been used therefor.
When using such glass mirrors, however, there have been a problem of breakage during transportation and a problem of increased construction cost because of high strength required for mounts on which the mirrors are to be mounted.
In order to solve such problems, it has been proposed in recent years to replace glass mirrors by reflective resin sheets (hereinafter also referred to as “film mirrors”).
The surface layer of a film mirror is required to have stain-proof properties and scratch resistance. As for the scratch resistance, the surface is required to be resistant to scratches in collision with sandy dust grain aggregates in a sandstorm and is also required to be resistant to scratches upon cleaning with a brush.
A composite film is known which protects against scratches upon collision with sandy dust by forming a soft resin layer having self-repairing properties as the surface layer of a resin substrate.
The surface layer made of soft resin had the following problem: Scratches due to impact of fine objects such as sandy dust do not occur but permanent scratches occur due to cleaning with a brush which involves hard scraping to such an extent that the elastic limit is exceeded.
JP 2004-314408 A describes a low reflection film which can protect against reflection due to outside light and is also excellent in dust resistance and which particularly has sufficient abrasion resistance to prevent the transparency from being impaired by abrasion due to friction and is also excellent in contamination resistance. However, the abrasion resistance is tested in order to evaluate the scratch resistance by scraping the film back and forth using white flannel and the performance required for the film mirror to be protected against surface scratches that may be caused by collision with sandy dust grain aggregates is not examined.